In flight simulators, such as helicopter flight simulators, there is a known way of obtaining a wide horizontal field (of 180.degree. or more) by means of projection systems collimated to infinity using a spherical mirror out of axis and a screen, that is also spherical, associated with a projector. By contrast, in the vertical direction, the size of the field attains hardly 40.degree. because of the conformation of the optic system. To enable the display of the image seen through the bottom windows of a helicopter, it is generally the practice to use a cathode-ray tube monitor with a system of display at infinity but, in this case, the field obtained through the monitor is inadequate.